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Search: id:A101781
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| A101781 |
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Lower bound of twin primes pairs whose digital reverse is also prime. |
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+0
1
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| 3, 5, 11, 17, 71, 101, 107, 149, 179, 191, 311, 347, 1031, 1061, 1091, 1151, 1229, 1301, 1487, 1619, 1949, 3251, 3257, 3299, 3359, 3371, 3389, 3467, 3527, 3767, 3821, 3851, 3917, 3929, 7349, 7457, 7547, 7589, 7757, 7949, 9011, 9041, 9341, 9437, 9857, 10007
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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17 is the lower bound of twin prime pair (17,19) and its digital reverse, 71, is prime.
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PROGRAM
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(PARI) twlrpr(n) = { for(x=1, n, y=twinl(x); z=eval(rev(y)); if(isprime(z), print1(y", ")) ) } twinl(n) = \The n-th lower twin prime { local(c, x); c=0; x=1; while(c<n, if(isprime(prime(x)+2), c++); x++; ); return(prime(x-1)) } rev(str) = \ Get the reverse of the input string { local(tmp, s, j); tmp = Vec(Str(str)); s=""; forstep(j=length(tmp), 1, -1, s=concat(s, tmp[j])); return(s) }
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CROSSREFS
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Sequence in context: A019386 A147251 A146473 this_sequence A101783 A078883 A109556
Adjacent sequences: A101778 A101779 A101780 this_sequence A101782 A101783 A101784
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KEYWORD
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nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Jan 26 2005
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